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~1.8-2.6 Ga--first red Banded Iron Formations (BIF's) - red and gray zones of oxidized iron layers of silica. Responsible for world's most important iron deposits. As soluble iron was used up, O2 began to increase in atmosphere, and CO2 decreased continued until ~2 Ga=first appearance of red beds (and appearance of ozone!) Red beds = shallow-water, river, or soil deposits in which the iron has combined with O2 to form red iron oxide Proterozoic rocks

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red beds=O2 increase in atmosphere BIFs decline, an indication that reducing compounds are disappearing from the oceans ( weathering as we know it was probably set up at this time Less CO2 more CO2 Proterozoic rocks

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Life in Proterozoic Until about 1.9 Ga we only have evidence of the simplest kinds of life - the PROKARYOTES – bacteria and blue green algaePROKARYOTES Requirements to be Life –self-replicating (DNA) –metabolism (chemical processes that convert food into energy) But at about 1.9 billion years we start to see fossils of much larger cells. These cells belong to the Eukaryotes - of which we are membersEukaryotes First sexual reproduction!

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Life in Proterozoic ~650 mya (0.65 billion) the first multicellular forms are present called the Ediacara assemblages seem to be elaborations of forms with –large surface areas –living in shallow relatively high energy environments –often in red beds.

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Life in Proterozoic Originally discovered in Pound Qtzt, Ediacara Hills, S. Australia; later found worldwide (including Piedmont area of NC) at low paleolatitudes. 0.59 - 0.7 by (590 - 700 my) impressions and molds of animals (associated with trace fossils)

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Animals with hard-shells appeared in great numbers for the first time during the Cambrian. The continents were flooded by shallow seas. The supercontinent of Gondwana had just formed and was located near the South Pole. NA=Laurentia N.Europe=Baltica